1. Field of the Invention
The present invention relates to the field of continuous-time filtering and Δ-Σ analog to digital converters.
2. Prior Art
Continuous-time filters which utilize feed-forward topologies, feedback topologies or both are used for various purposes. One such use is in receivers in wireless networks. Such filters generally use multi-stages of transconductance amplifiers and integration capacitors. Because of process variations, the poles of the loop filter will change accordingly, leading to degraded performance or even resulting in instability.
The conventional wisdom is to tune or trim the integration capacitors (C) and/or transconductors of each stage (GMi, i=1, 2, 3, 4). There are several drawbacks with these previous methods:
1) Tune/trim of the transconductance (GM) of each stage will affect the noise performance of the overall filter/modulator, especially for Gm1 (the first stage);
2) For multi-band/multi-corner (multi-standard) frequency applications such as wireless cellular, the GM'S and C's have to be adjusted for each standard, which results in inefficient implementations, extra complexity and degraded performance.